An insight into torque production and power factor in transverse-flux machines

Abstract

Abstract-Despite transverse flux machines (TFMs) being intrinsically three-dimensional, it is still possible to model them analytically using relatively simple models. This paper aims to provide an insight into the behaviour of TFMs using a compact equation, which relates torque to the electric and magnetic loadings of the machine and a flux factor. The flux factor is also used to estimate the flux linkage and therefore the power factor of this kind of machines. It is shown that the low power factor of TFMs is not only due to leakage but also due to the nature of the electromagnetic interaction that takes place. The TFM developed at the University of Southampton is used as the basis of a case study to illustrate the trade-off between torque density and power factor, and to provide some design guidelines. The analytical results are verified using finite elements analysis and experimental data.

Analysis of Transverse Flux Machines Using a Virtual Mutual Inductance Approach

“…TFMs tend to have a low power factor; in [18] this topic is studied in detail. The conclusion is that besides the leakage, which is relatively high in these machines, the main cause of the low power factor of TFMs is their ineffective use of magnetic flux [19]. This can be easily seen in the fact that during the calculation of the virtual mutual inductance one of the equivalent current loops has a strong positive flux linking while the flux linking with the other current loop is in the opposite direction.…”

“…However, since there is one additional pair of poles the electrical frequency has to increase and so does the reactance. This shows that the low power factor of TFMs is not due to leakage in the classical way but due to the ineffective use of the magnetic flux as it was mentioned earlier in this paper and discussed in [18], [19]. If the design optimisation is done only considering torque, as many authors propose [48], [49], [50], the optimal machine would have N c = 24 C-cores.…”

“…The relationship between torque and power factor was studied in [19]. However, in that publication the amplitude of the back emf was simply estimated by conservation of energy and the flux linkage was not calculated formally.…”

“…However, TFMs tend to have a complicated topology with a threedimensional flux path, which makes the task of modelling and understanding the behaviour of these devices difficult. Additionally, TFMs tend to have a low power factor, which has hindered their acceptance [18], [19].…”

Transverse flux machines as an alternative to radial flux machines in an in‐wheel motor

“…In recent years, several researchers have considered the use of TFMs for direct drive or in‐wheel applications using analytical and FEA methods [5–7]. Here, results were obtained from 3D FEA.…”